Process for preparing methine dyes



Patented Aug. 18, 1953 PROCESS FOR PREPARING METHINE DYES 7 William W. Williams, Easton, Pa., and Albert F. Strobel, Phillipsburg, N. J assignors to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application November 6, 1950, Serial No. 194,382

" Claims. (omen-'46s This invention relates to a novel method of preparing methine dyestuffs which correspond to the general formula:

R1 H /CN 34 \OOOR wherein R, R1 and R2 represent lower alkyl radicals.

Dyestuffs of the aforementioned type have heretofore been prepared by refluxing, in an mert organic solvent medium, a para-dialkylammo benzaldehyde of the formula:

with a cyanoacetic acid alkyl ester of the formula:

COOR

wherein R, R1 and R2 have the values given above, in the presence of a small amount of piperidine, followed by cooling whereby the desired methine condensation product crystallizes out, filtering, washing and drying. This product is then usually purified by recrystallization from solvent media and drying, after which it is reduced to a dry powder by grinding with dispersing agents, etc. This typical process is disclosed, for example, in Patents 1,950,421 and 2,206,108. Such a process is open to objection for various reasons. Excessive kettle space relative to the volume of reactants is required because of the large volume of inert solvent employed. Crystallization is a time-consuming and tedious operation, as well as filtration, washing and drying. The use of an inert solventis costly, in addition to presenting fire and health hazards and various technical difiiculties. Recrystallization requires the use of additional solvent.

It is among the objects of this invention to provide a process for preparing the aforementioned methine dyestuffs which is substantially quantitative, simple, efiicient and economical, and which will eliminate substantially all of the objections applicable to the presently employed processes. Other objects will become apparent from the following description of our invention.

We have found that thereaction can be run almost quantitatively by condensing the reactants in the absence of an inert solvent at a temill perature sufficient to maintain the starting products and the reaction product in .a liquidcondition until the condensation is completed. .Piperidine or similar compound is necessary as a catalyst for efficient reaction. By the use of our new method larger charges can be run in the same kettle space since the volume is reduced considerably. Slow crystallization, filtration, washing and drying are eliminated, as well as the increased fire and health hazards and cost of usin solvents. The dyes obtained have dyeing properties (such as light-fastness, washfastness, exhaustion from dye bath, yield, degree of dispersion, and tar test) as good as, or better than, the corresponding dyes prepared by the solvent method. In some cases, brighter shades are obtainable in fabrics dyed therewith. Because of the high efiiciency of the condensation, which is almost quantitative, purification steps such as washing, extraction and recrystallization, are unnecessary. When the condensation has been completed at the required temperature, the mass need only be cooled to solidify and ground with dispersing, emulsifying and/or wetting agents and the like to produce the finished dyestuff powder.

The invention is further illustrated by the following examples, although it is to be understood that they are illustrative and not limitative. Parts are by weight unless otherwise specified.

Example 1 250 g. of crude p-diethylamino benzaldehyde (71%) was melted on a steam bath, warmed to 75 0., and filtered through a Biichner funnel. 21 g. of insoluble material remained on the filter paper. The filtrate was transferred to a 1- liter round-bottomed flask, warmed to C. and 4.0 g. of piperidine was added. With good agitation, at 80-90 C., 113 g. of ethyl cyanoacetate was dripped in over a 2-hour period. The material'was stirred 1 hour longer at 80 C. after complete addition of the ethyl cyanoacetate, then stirred 3 hours at C. The molten mass was poured on a fiat dish and it set up to a hard mass in a short time. 302 g. of material were obtained which consisted of the substantially pure compound represented by the formula:

CzHa

licorice root) and 50 g. Aquanol SO (sodium salt of a sulfonated long chain alcohol sold by the Beacon Company). Agitation was started, then 40 g. water added, giving a thick mass for kneading. The mill was run for 3 hours until the product was dry. -l90 g. of *dispe'rsedmaterial was recovered-from the. mill.

The product had dyeing properties equal to those of the product produced by the solvent method.

Example 2 Q 250 g. of p-diethylaminobenzaldehyde"Q'll%) was placed in a 1-liter round-bottomedz-flask and to it was added 100 g. of methyl cyanoacetate. Over a hour period the mixture was warmed to 70 C. At 70 C., over a 1 hour period 4 ;g.of piperidine was gradually added, keeping the temperature at 70 C. by alternate heating and cooling. Then the temperature was raised to 95 C. andzma'intained at this point for 3 hours. The 'moltentmass"-waszpoured on a fiat dish, cooled -toz=room temperature, and crystallization initiated .bwscratching the side. of-the dish. The material zgraiclually crystallized to a hard mass which con- ESiStEd :of'the substantially. pure compound reprezsentedhy the formula:

(333:5 /CN .CzHs C O O CH;

"Dispersion was carried out in the same way as '-in Example 1.

The-product dyed cellulose acetate in a greener, brighter shade'than 'didthe analogous product *prepared'using the solvent method. Light-fastness, dispersion, and tar tests were correspond- '-ingly equal in both products.

Theprocess as described hereinbefore may be modified and/or adjusted as appears hereinafter.

"Since the condensation is practically quantitative-substantially equimolar proportions of the *reactantsshould be employed. Proportions outside of this range are undesirable as the amount "of-reactant in excess of these proportionswould 4.)

remain unreacted .and would require removal from-the'finished product by otherwise unnecessary purification procedures.

lnigeneral,"temperatures of 70 to 110. C. prescribe'the outside operative limits. temperature would result in separation of one of the.starting products or reaction product before thecondensation has beencompleted. Too high a temperature Wouldtend to distill off a part of the reactionmixture which .would be undesirable 50 in throwing the reaction out of equilibrium. Such .un'duly .high temperatures have likewise been "founidto. produce dyes giving duller shades. The optimum temperature in any particular instance will obviouslybe dependent mainly upon the melt- 'ing points and intrasolubilities of the components of :thelreaction mixture. vPart of the water resiiltingirom-the condensation will vaporize out :of the reaction mixture during the condensation, but any residual amount of waterremainingin *the hardened mass would not be detrimental to the properties of. the finished dyestuiT.

The length of itme of the heating operation necessary to carry the condensation. reaction to completion will depend mainly upon the nature of the components of the reaction. mixture and the temperature employed. Usually about three -hoursqofrheating after-all of the components of :the; reaction .mixture have been added are sumecient to: produce a complete condensation, al-"' Too low a a0 Theamount. of catalyst employed must be sum- "cient'to'efiect complete condensation between the entire :amounts of ir-eactants present. However, tooslargeaan'amount of catalyst would necessitate removal of excess catalyst from the reaction --product. 'Obviously, the minimum amount of catalyst oper-ativeto effect complete condensationis desirable. In general, about 2% to about 4% ,of piperidine on the weight of the benzaldehyde is adequate to produce the results desired.

Other catalysts are used in equivalent amounts afterproper adjustment.

Instead of the benzaldehyde employedin the examples, there may be-used other lower p-dialkylamino benzaldehydes, such as para-dipropylamino benzaldehyde, para=dibutylamino benzaldehyde, and para-diethylamino' benzaldehyde, in addition to the mixed benzaldehydes such as .parae-meth-ylethylamino benzaldehyde, paramethylbutylamino benzaldehyde and other lower dialkyl combinations thereof. Ring-substituted benzal de hydes are likewise to be understood as .included within the scope of the invention and claims provided the ,substituentsare hydrocarbon and/or other inert groups which are not detrimental with respect" to the desired reaction,

solubility, melting 'point, properties of the reaction p-roduct, and the like. .Instead of the methyl and ethyl cyanoacetates, there maybe used other lower alkyl esters, such as the propyl 40 and butyl cyanoacetates.

Since the cooled solid mass resulting from the condensation is in a substantially pure state, purification steps ordinarily necessary at this stage may be dispensed with and the solid mass ground directly into afinished d-ye powder in well known :manner using dispersing, wetting and/or emulsityingagents andlwater. While an alkaline secondary-extract-of li-coriceroot has been found very satisfactory, other similar assistants maybe added thereto orsubstituted-therefor. Alkaline "assistants areto be'preferred.

l @ur'invention has-:been-described with respect to certain pref-erredem-bodiments thereof but -variousmod-ifications and-variations within the r e t co e of the invention will become apparent to'thoseskilled in the art. It is accordingly understood that such modifications and variations-are to be considered as within the pur- :view of this application and the scope of the apmended-claims.

Weclaim:

:l.- -A= process foi producing a, compound of the formula:

.b heatin a. comp sit on cQmprisin su s anQ aHy mul and a compound of the formula:

COOR together with a small amount of an alkaline catalyst, in the absence of an inert solvent, at a temperature sufficient to maintain the starting products and reaction product in a liquid condition until the condensation is completed, R, R1 and R2 in the above formulae being selected from the group consisting of lower alkyl radicals.

2. A process for producing a compound of the formula:

R2 o 0 R by heating a composition comprising substantially equimolar amounts of a compound of the formula:

and a compound of the formula:

COOR together with from about 2% to about 4% by Weight of an alkaline catalyst on the weight of the benzaldehyde, in the absence of an inert solvent, at a temperature sufficient to maintain the starting products and reaction product in a liquid condition until the condensation is completed, R, R1 and R2 in the above formulae being selected from the group consisting of lower alkyl radicals.

3. A process for producing a compound of the formula:

H /ON Rz C 0 OR by heating a composition comprising substantially equimolar amounts of a compound of the formula:

R2 and a compound of the formula:

C335 /ON 02H; C O 0 0211 by heating a composition comprising substantially equimolar amounts of para-diethylamino benzaldehyde and ethyl cyanoacetate together with about 2% by Weight of piperidine on the Weight of the benzaldehyde, in the absence of an inert solvent, at a temperature sufiicient to maintain the starting products and reaction product in a liquid condition until the condensation is completed.

5. A process for producing a compound of the formula:

Get /CN 02135 C O O CH;

by heating a composition comprising substantially equimolar amounts of para-diethylamino benzaldehyde and methyl cyanoacetate together with about 2% by weight of piperidine on the weight of the benzaldehyde, in the absence of an inert solvent, at a temperature suflicient to maintain the starting products and reaction product in a liquid condition until the condensation is completed.

WILLIAM W. WILLIAMS. ALBERT F. STROBEL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,950,421 Wahl Mar. 13, 1934 FOREIGN PATENTS Number Country Date 606,962 Great Britain Aug. 24, I948 OTHER REFERENCES Adams et al., Org. Reactions (Wiley) vol. 1, DD. 234-235 (1942). 

1. A PROCESS FOR PRODUCING A COMPOUND OF THE FORMULA: 